The invention relates to a clock data recovery scheme, and more particularly to a clock data recovery apparatus and corresponding frequency control circuit.
Generally speaking, a conventional clock data recovery device ideally can be adopted to track frequency offset for a data signal to lock the frequency of the data signal. The conventional clock data recovery device may include a single low-pass filter. However, practically, the conventional clock data recovery device is limited by the band width of its low-pass filter, process variation when manufacturing, and/or a severe environment condition such as rapid changes in temperature. For example, the conventional clock data recovery device inevitably cannot reduce more noise if the single low-pass filter is implemented with a wider bandwidth since the wider bandwidth can filter out less noise. However, if the single low-pass filter is implemented with a narrower band width, the conventional clock data recovery device certainly cannot track larger frequency offset of the data signal. This problem will become more critical if the conventional clock data recovery device is used in the severe environment condition.